This invention relates to a portable dolly operable manually by a single person for safely transporting a relatively heavy load up or down various staircases having steps of different heights and depths.
A portable dolly is commonly used for transporting a heavy load such as furniture or a large appliance. The dolly is provided with rotary wheels and the load is mounted or rested securely on a support shelf on the dolly so that the load may be transported by simply wheeling the dolly from one location to another location on a ground or a floor. However, it has been problematic to move a heavy load up or down a staircase, since it is not possible to push the dolly up the steps of the staircase and it is very hazardous to attempt to push the dolly down the steps in such instances since it would drop from one step to a lower step. The drop could cause damage to the dolly and the load and also the dolly could continue to roll down the steps uncontrollably due to the falling momentum. Therefore, it is necessary that the dolly with the load resting thereon must be lifted and carried up or down the staircase. Such operation is difficult, if not impossible in most instances, for one person to carry out.
There are some dollies such as that shown in U.S. Pat. No. 2,633,363 issued to J. M. Marshall on Mar. 31, 1953 and U.S. Pat. No. 3,698,501 issued to E. S. Gross on Oct. 17, 1972 which are provided with a star-shaped rotary support having wheels mounted at its corners. The rotary support is rotatable to position the neighboring wheels at its corners on consecutive steps of a staircase such that the dolly may be pushed up or down the staircase. In both these devices, the above stated problem of the dolly continuing to roll down the steps by momentum still exists, and the dolly would still roll down the steps by the wheels of the star-shaped rotary support. Furthermore, the Gross device has an electric motor incorporated therein, which can be energized to drive the star-shaped rotary support. Such dolly is rather complex in structure and the motor and the associated driving gear mechanism would invariably increase the weight of the device such that it would be difficult to handle by a single person. Moreover, since the electric motor must be connected to a nearby electrical supply with a power cable for its operation; it is awkward to use or is useless if no power supply outlet is close by. Also, the star-shaped rotary support in both devices shown in these patents has a fixed size so that it can only operate on a staircase having steps of a predetermined height and depth.
It is a primary object of the present invention to provide a manually operable dolly which is operable for transporting a load up or down a staircase with ease in a controlled manner.
It is another object of the present invention to provide a dolly which is operable on various staircases having steps of different heights and depths.
It is another object of the present invention to provide a dolly having a relatively light weight and may be operated by a single person.
It is still another object of the present invention to provide a dolly having a simply construction and is easy to operate.